1. Field of the Invention
The present invention relates to a partially reinforcing method and apparatus of metal material for reinforcing a part of metal material.
2. Description of the Related Art
In general, selecting a material of a formed body, the material having hardness or yield strength satisfying the max value of a required strength is considered. Alternatively, a material which can be subjected to a heat treatment after a press-forming to reinforce the whole formed body is selected.
However, if the material is selected in view of strength of a part requiring the largest strength, following disadvantage may occur. The press-forming property of the material is lowered as a whole, and in the worst case, the material can not be formed. In addition, using the material having high strength is expensive and uneconomical, since even in the part not requiring the larger strength, the formed body has the thickness larger than the thickness naturally required.
On the other hand, there is a method in which a pressed formed body may be subjected to a heat treatment to increase the strength. In this case, the heat treatment process needs additional equipment and the step, so that the cost is increased.
As the reinforcing method of the limited part of the formed body, the part requiring the strength has been subjected to a shot blast processing after the press-forming, has been known. In addition, a method for increasing a plate thickness of the part requiring strength has been known (refer to Patent Publication No.1). For this purpose, the strength required part of a press-formed body made of steel is subjected to a flame spray to form a flame spray film. A strengthening method of a work by heating a part requiring the strength higher than other part and then quenched, has been known (refer to Patent Publication No.2).
By the way, to satisfy requirement of lightweight of a vehicle, thinning the constructing member, or forming the constructing member by a lightweight material such as the aluminum (aluminizing the constructing member) have been tried. For example, forming a suspension member or a frame member of a vehicle body which have been formed by the steel formed body is formed by the aluminum formed body for lightening (for light-weighting).
However, the hardness of the aluminum is smaller than that of the steel. For this reason, at the position where the suspension member formed by the aluminum alloy is contacted with the bushing attached to the lower arm and the upper arm, there is a fear that the slide surface of the suspension member may be worn due to sliding of a bushing, when the vehicle is running. To avoid such disadvantage, larger-size bushing is used to decrease the limitive surface pressure thereof, or the aluminum alloy of the larger strength has been used for the suspension member. These manners, however, increase of cost of the bushing and the suspension member, and lower of the forming property of the suspension member.
[Patent document 1] Japanese Patent Laid-open No.7-3427
[Patent document 2] Japanese Patent Laid-open No.2002-241835